Technical Abstract:
Claypan soils have a highly impermeable argillic horizon containing 50 to 55% clay about 15 to 30 cm below the soil surface that can restrict air and water movement and retard plant root development. These soils can be problematic concerning herbicide contamination of surface runoff during high rainfall periods when the soil above the claypan becomes saturated. Investigations of cover crops on claypan soils are limited, and more information is needed to assess adaptation and weed management on these soils. Integrating soil-applied biological control organisms with cover crops for enhanced suppression of weed growth to decrease herbicide use also needs attention. Objectives were to determine the effectiveness of several spring- and fall-seeded cover crops and soil applied biological control bacteria on weed growth and distribution on a claypan soil. Various cover crops were established on a claypan soil in north-central MO and were combined with or without deleterious rhizobacteria (DRB) selected for growth suppression of giant foxtail and velvetleaf. Total biomass accumulations were greatest for rye, wheat, barley, sweet clover, and annual ryegrass with commensurate reductions in weed biomass. Soil inoculation with DRB combined with cover crops reduced weed biomass compared to noninoculated plots. Brassica cover crops varied in biomass production (oilseed rape > green mustard > canola > Tatsoi mustard) but appeared equivalent in selectively suppressing Amaranthus species and suppressing late-season giant foxtail, suggesting involvement of allelochemicals released from residues in soil and/or on the soil surface.